Characterization of Cassava Starch-Stearic Acid Complex Nanoparticles and Stability of Pickering Emulsions Stabilized by It

In order to study the feasibility of applying cassava starch-fatty acid complexes as a Pickering emulsion stabilizer, complex nanoparticles with complexing index (CPI) of 2.74%, 9.17% and 27.66% were prepared by mixing cassava starch paste containing 78.65% amylopectin at 95 ℃ and stearic acid followed by alcohol precipitation. The three complexes had an irregular spherical-like shape under field emission scanning electron microscopy (FESEM), and their average particle sizes, determined by a laser particle size analyzer, were 315.35, 348.19 and 427.60 nm, respectively. The X-ray diffraction pattern of each of the complexes showed two peaks at 13° and 21°, which were characteristics of the V type crystal structure, and the crystal content increase with increasing CPI. Their deconvoluted infrared spectra exhibited changes in short-range ordering at 1047, 1022 and 995 cm^-1. The contact angle of the particles with the highest CPI was 60.30°. The three complex nanoparticles stabilized Pickering emulsions for more than seven days compared to less than two days with starch nanoparticles. The complex nanoparticles with CPI of 27.66% stabilized emulsions best. The addition of the complex nanoparticles with CPI of 27.66% at levels above 0.1 g/100 mL resulted in the formation of an emulsion with an oil-to-water ratio of 1:9 (V/V). The emulsion with this nanoparticle at 7 g/100 mL exhibited an improved stability for 60 days without creaming or phase separation. Moreover, no significant changes in the droplet size distribution were observed. The emulsion was stable at pH 5.6-9.0 and not affected by NaCl concentration in the range of 0.01-0.1 mol/L. The emulsion maintained its morphology well after being heated to 80 ℃. These results suggest that the complex nanoparticles are a potential Pickering emulsion stabilizer.